The reduction of air turbulence and of drag associated with a vehicle which is towed by another vehicle, is a concern which is widely recognized. By way of example, the use of structures on a front vehicle to reduce turbulence and/or drag associated with a taller rear vehicle is a rather common occurrence on the roadways. Some examples of rather unconventional structures of this kind can be found in, for example, Saunders, U.S. Pat. No. 3,348,873, Stamm, U.S. Pat. No. 2,863,695, Woolcock, U.S. Pat. No. 4,199,185, and Taylor et al., U.S. Pat. No. 4,156,543.
The advantages of attempting to reduce turbulence and/or drag by structures altering the flow of air along the sides of the vehicles has also been recognized. Saunders, cited above, provides vertical structures, behind a tractor unit, which extend beyond the sides of the unit. Their main purpose is to reduce body sway of a towed trailer due to the entry of a side wind between the tractor and the trailer. Where Saunders provides structure at the sides of, as opposed to behind, the tractor, such structure is provided by forming the sides of the tractor with recesses to direct air, first, inward, and, then, outward away from the gap between the tractor and the trailer. Stamm, also cited above, provides, in effect, conduits, each having an inside plate and an outside plate, near the rear of the tractor, to direct air streams to similar conduits near the front of the trailer. The inside plate of the conduit structure is joined to the tractor along one of its two large surfaces. The outside plate is attached to the inside plate with substantial space between the two plates. Such space is required to accomplish the conduit-type structure and the air stream effect.
Gulich et al., U.S. Pat. No. 3,878,914, provides vertical structures at the rear corners of a tractor, each providing three vertical concave surfaces. The primary purpose of the structures is to prevent engine exhaust from going forward to the passenger compartment, although there also is some air flow control.
Taylor et al., cited above, provides side curtains across the space between a tractor and a trailer; and Woolcock, also cited above, in the context of controlling the flow of air over the top of a tractor-trailer, also recognizes the desirability of directing air flow around a trailer which is wider than its tractor (FIG. 5).
Harris, U.S. Pat. No. 2,396,506, is less relevant than the above patents.
The present invention, as with the art in general, recognizes the substantial advantages to be garnered by reducing turbulence and drag associated with a towed vehicle by altering air flow at the sides of the towing and towed vehicles. However, it also recognizes and takes account of a number of other important concerns. First, it recognizes the advantages of simplicity of design and of construction of the structure which is to affect such air flow. Secondly, it recognizes that the capability for easy mounting and de-mounting of the structure is a significant concern, including minimizing any alterations of a vehicle on which the structure is mounted. Thirdly, it recognizes the need for structure particularly adapted to configurations other than the conventional tractor-trailer arrangement.